Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plumcrazyfx on March 06, 2018, 06:11:46 am
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So my experience is that I have a Traynor YGM-3 that has 450v on the plates of the EL84s. It sounds great but I worry about tube life, reliability, etc. even with using 6P14P-EVs. So I went and bought some adaptors to use JJ 6V6S in place of the EL84s. Sounded great - but NO TREM!
So now I'm thinking of building a 6G2 or 6G3 out of a Hammond AO-43 chassis and I would like to use the original EL84s. So I'm anticipating the same issues with the trem not working right. So my basic question is - What parts of the trem circuits should I be looking at to tweak to get a trem designed for one tube to work with a different tube type?
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So I went and bought some adaptors to use JJ 6V6S in place of the EL84s. Sounded great - but NO TREM!
EL84s only need about -15v bias but those 6V6s will need about -30v or -35v to be happy. You're cooking those 6V6s if you didn't modify the bias circuit.
If you build the 6G2 or 6G3 according to the schematic the tremolo will work just fine.
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I put in bias pot and adjusted accordingly- just no trem.
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What dc voltage do you measure on pin 5 of the 6V6s? What is the amplitude of the tremolo signal at pin 5 of the 6V6s?
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FWIW: my solution to hi voltage Traynor: i) 12V bucking tranny to knock down wall voltage (keep at least 5.3 heater volts); then ii) inductive power resistor in the B+ rail to drop another 50VDC. This got me from 410VDC > 280VDC on EL84 plates. Starting @ 450 you should be able to get down to about 320 which I think would be good enough.
OTOH, the amp will probably work fine as-is. The problem you pose -- short tube life -- is purely theoretical at this time; especially since guitar amps are typically in use for short time periods. Best to keep a spare set of tubes on hand for amp. In the unlikely event that tubes fail too often, you can do mods then.
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This was more of a theoretical question based on the Traynor experience as to whether I should expect to have to tweak the trem if I build a 6G2 or 6G3 with EL84s. Or looking for an explanation as to what tweaks I would do to make them work with the trem.
I don't have the measurements on the Traynor- as soon as the trem didn't work with a drop-in 6V6 I kind of abandoned that method and used a bucking transformer + 6P14P-EVs + increasing screen resistors for my piece of mind.
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I seemed to remeber it from befote when I tried it and I looked and Yellow Jackets have a disclaimer that the trem won't work if you use the converters on bias type tremolo (they mention the AA1164). My converters don't have any resistors adjusting voltage, just rearrange the pins. I assume something needs to be done to match bias to oscillator?
I also did a quick look at both the 6G3 and Traynor tremolos and they are very similar.
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This was more of a theoretical question based on the Traynor experience as to whether I should expect to have to tweak the trem if I build a 6G2 or 6G3 with EL84s. Or looking for an explanation as to what tweaks I would do to make them work with the trem.
I answered that question also.
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So a 6G3 with EL84s will work fine if biased correctly. But we can't know why the Traynor won't make the conversion to 6V6s without voltages etc? Okay, thanks.
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EL84 tubes require less bias voltage than a 6V6. That also means that a smaller signal (guitar or tremolo) is required for the EL84. So if you build a 6V6 designed amp but use EL84s instead, you will have plenty of guitar and tremolo signal for those EL84s. In fact you will have too much signal and will likely need to run the volume and intensity lower to prevent overdriving the EL84s. Overdriving any tube with too much tremolo signal does not sound pretty. You will also need to modify the bias supply to provide the proper bias for the EL84s.
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Thanks.